Dropback selector for telephone systems



July 14, 1959 w. w. PHARls ETAL nRoPBAcK SELECTOR FOR TELEPHONE' SYSTEMS Filed Feb. 25. 1957 2 snags-sheet 1 H ,H mw S www TAZ nlv NHT ,o m u WP@ E T I N E y wml R www?? m ssm m MTM m ..I |||||l :l l Il I|||| l.|| L f LN 'R H mm L+ m we O 5 R ,w N P mn. m w w Y -l i!-fnvllli L B w w1 E. m 9 .W m w Y e T M M H Q O E 67 c l. l. T. l D I +43 r D W L E Q (QW. W. m m 1 s D @l Il# h.- u IIIIIII' E m E .v R 65) Wu HH m Iu. 1111 :u 1| I #im H E H m l l I l Il n n w12 M awlm@ j m m m R s s s H w. s I m F m m w HSS w. w. PHARls ET AL DROPBACK SELECTOR FOR TELEPHONE SYSTEMS /w-'zll July 14, 1959 Filed Feb. 25, 195'7v 8 l 7 1 2 I l 8 b 6 7 6 o 2 2 Ao 49 2 L6 6 VA 22 L E2 2 n lllllllllllllll l1 Ilm- /l v 1 lill-: N .V 2 A C 4 .lTs 2 22 I2 T 2 XX 55 S wlw. a m 1w-USI 2 H A R T O N U H i l /273 {p2-r4 I 269 cANcl-:LB

United States Patent DRQPBACK SELECTOR For TELEPHGNE SYSTEMS .4 dans (C1,- '11a-18) This invention relates to d ial telephone systems in general and more particularly to selectors of a multiple dropback type for use in such systems. y

In previous selectors yof the multiple dropback type, such as the Vstep-by-step type selector disclosed in the application of William W. Pharis, Serial No. 312,686, tiled October 2, 1952, various combinations of digits absorbed .during the multiple dropback process prior ltothe unlocking operation of the selector are described. Thus, it is old `in the art to provide a selector which unlocks with respect to all levels after dropping back in response to the kreceiptof rst Vand second oice code digits of various .values and whichalso unlocks with respect to a particular 4level upon ,the receipt of arstrdigit corresponding tothe .particular level and different from therst otice code digits. With this arrangement, lthe selector may be caused `to advance within any level following the receipt of the office code .digits and a third level selecting digit and withinithe .particular level following thereceipt of the singlelevel 4unlocking digit and another identical digit. However, Vthe apparatus conventionally supplied vfor achieving this operationhas tended to be both complex and expensive. This has markedly increased thetot'al Icost of systems involving such selectors. for use in step-by- .step system .because the dropback controlling apparatus `must be yindividualto the apparatus suppliedwith 4each selector.

Accordingly, it is an object of our invention to provide a new andtimproved multiple dropback selector of the above type. v

Another object of our invention is to provide a dropback selector ofthe above type in which the apparatus per selector` is kept at a minimum.

Another object of our invention is to minimize the dropback control equipment per circuit by the use of two-step relays.

-We accomplish these and other objects by providing a selector having a directively operable switch which may be moved fromitsnormal position in a primary direction Yto select anyone of a'plurality of levels. The levels include Vparticular first andlseciondlevels. The selector includes means thereafter automatically operable for'moving the switch oit-normal in a secondary direction within the s'elected level in order to lcause the selector to hunt for`an idle line terminated Within the selected level; The selector also includesmeans for returningthe switch 'toits normal position. i

i Our invention resides in providing in combinationvvith the above-named elementswdropback means including a relay having a normal position and operative through rst and second-steps for causing multiple dropback operation vofithe switch. .f'Ihedropback means is controlled by primary movement of the switchforselectively operating v,the relay-through itsiirst or second step` and forthere- ,after` operating .the returning means. Y The relay operated initiating the automatic operation of the secondary direc- 2,895,011 Estates? July 1.4 1915? tion moving means. In the icase where the relay has been operated through its second step,"t`he relay is e'e'ctive in response to a subsequent primary movement of the switch to arly of the levels xfor starting the automatic operation of 5 th secondary'direction moving means i For aVV better understanding of "our"invention, reference is nia'de inthe following description to drawingsi attached to and forminga 'part of the` present specication, in

y s.V l and 2, placed in numerical order, left to right, shvv" a schematic representation of a'rnultiple'dropback yPower for operating the selector is drawn from a direct current source, such as a battery' The molstlpositiveplat'e VQifterniin al of the battery connected toground, and is hereinafter referred to'as groundl and in the-drawings' as`L(`L|-`)`.` The' most negative, ungrounded plate or tei"- minal of thjehattery ishereinafter kreferred to Vas'fbattery :and inthe drawings as 'i l""lf dropbackselector circuit of the invention will be r described inconnec'tion with 4the 'use' of 5a" directively Ystejpped'lswitch offthe type sold under the trademark """XY,`' althoughfit will bev understood fthat other yforms Vof tively operated' stepping' switches maybel used by 's'e'yskilled 'in' the fart to 'practice ourA invention. De- Y 's ofthe switch are' described yinfthe patent to Frank A. `Mo lis, NoLy 2,567,650, issuedfS'eptember' 11,1951, fto 'vvhlchfrev rence may be'made. 'Briefly described, howf i t Ich includes a main seit of four wipers or con- 30 aan.. es. "These-hints; Wm. W212; WzIpr-lnd 'VV/214, corresponding toitip,"ring, "sleeve," and hunt sleeve, are mounted on a carriage forprirnaryand secondary difrect,ion`inoxrefnient'sv inthe same plane. Banksof Wirecon- 'tacts are positioned in levels opposite each stepposition-to [which thejwiper set may be moved in *its primaryfdire'ction. Eachfof these levels contain sets of tipglring,vsleeveoand fhnt sleeve Contact 'wires forengagement Aby the`corr'e- 'sponding wipers. The vcontactwire setsjare-sp'aced apart from 'each other, andV one setA correspondsjto each second f d'iietionstep position of the Wiper set. `4

` Iniaddition tothe main Wiperset', level marking means including an auxiliary wiper Aset` (AW20 and'AWZl) and auxiliary `wrirebanks AAWB20 and lAWBZI are provided for indicating thex level to' whichthe main'wiper set is advanced in its4 primary direction. Thus, each of the wires within each kauxiliary bank correspondswto" one of'the A4levels, `and one s et lof( auxiliary wirebank Wiresis engaged .p by `:the correspniding auxiliary wiper set brush when the `main*wiper sethas been moved in its primary direction.

Inordker to move the switch in the primary andsecondarydirections, primary and secondary magnetsP110 and ,$110, respectively, are provided. In addition, means in- Hc dingrelease magnet vRL110 isprovidedto restore the ,Jperslets, ymain and auxiliary, to normal position under Spring action.'V Magnets P110 and S110 fare provided ,Y withint'errupter springs orf break contacts P111 and S111, l respectivrely, which areY opened when .the corresponding umagnet is energized. The switch is also provided with primary and lsecondary oil-normal contacts which'oper'ate wh,en, the switch moves off-normal in ei'th'erthe primary I or secgpnglary direction respectively. -Overflow 'contacts f are providedtobe operated fwhen the'switch is stepped Ain theseondary direction beyond the last set of Contact f vviresvin `anyflevel lf or disconnecting the -moving magnets fromztheir Venergizingucircuits in 'order to prevent useless stepping of the switch. `In the drawinghthe various offnormalinterrupter and overllowswitch 'contacts have been,shownl detached from their respective'op'eratingele- .lnaeritsd and they are identified'by prex lettering such as ;:PQNQOF, SON, etc. "Also as shovvnlinthe ,drawingQthe auxiliary Wipers together :with'ftheir'associatedcontct wire banks are shownin detailii order' tliaftlie"wiring 3 connected thereto provide the multidropback operation featured in our invention may be shown. However, the remaining contacts and details of the selector switches have not been shown inasmuch as they are not required for an understanding of the invention.

Seizure of the selector It is assumed that a connection has been extended to the selector shown in Figs. 1 and 2 by directively operating/the preceding switch train including selector SS110, and that after switching relay S115 within selector S8110 has operated under these conditions, the completed calling party loop bridged across incoming line conductors T1 and R1 operates calling bridge relay 110 over the following circuit: from ground through break contacts 141, PON111, 261, 271, and OF113, the upper winding of relay 110, break contacts 131, wiper T2, make contacts S111, conductor T1, the calling line loop, conductor R1, make contacts S112, wiper R2, break contacts 133, and the lower winding of relay 110 to battery. Operation of calling bridge relay 110 energizes an obvious operating circuit for release delay relay 120 at make contacts 112. Primary delay relay 140, a slow release type, is also energized from ground through make contacts 112, break contacts PON115, and the upper Winding of relay 140 to battery. Relay 140 thereupon operates and is elective at this time for connecting dial tone to the calling line loop. The tone is induced from a dial tone source through winding IND112 to winding IND11 and from there passes through make contacts 142, break contacts PON111, 261, 271 and OF113, the upper winding of relay 110, and break contacts 131 to the incoming conductor T1 in order to audibly indicate the readiness of the equipment to receive dial impulses from the calling line loop.

Operation of slow release relay 120 connects ground through make contacts 124 to the master ground lead and S bank and wiper S2 to preceding selector S8110 to hold the preceding switch train including selector S5110 in operated and busy condition while the call is in progress. Operation of relay 120 also fully lights monitor lamp L110 from ground through make contacts 127, break contacts 139d and through the monitor lamp L110 to battery in order to visually indicate that the seizure of the selector has been completed.

Stepping the switch in its primary direction Assuming that it is desired to advance the selector to the second level, which is characterized by wiring connected to AWB20 in order to provide secondary direction trunk hunting at the conclusion of the first digit in the manner to be described, the calling bridge relay 110 restores once for each of the ltwo digit impulses transmitted over the calling line loop to the selector; thereupon, magnet P110 steps the main wiper set, W211-W214, to the second level by connecting ground through break pulsing contacts 111, make contacts 121 and 143, and the winding of magnet P110 to battery. The lower winding of relay 140 is similarly energized from ground from the same source during impulsing. The operating circuit of relay .140 including the upper winding is opened at break primaryk ofi-normal contacts PON115 upon the first step of the switch in the primary direction. However, relay 140 remains operated while ground pulses are being applied to its lower winding due to its slow release characteristics. At the end of the impulsing operation, relay 110 comes to rest in its operated condition, so that the energizing circuitsof magnet P110 and the lower, holding winding of relay 140 are opened at break contcats 111 for a time interval suicient to allow relay 140 to release. The release of relay 140 indicates the end of the primary direction advance, and that the selector is in condition to initiate a secondary direction movement or a dropback I operation in the manner` to be explained.

Stepping the switch in its secondary direction at the end'I of the first digit At the completion of the above-described primary stepping operation, relay 140 restores to complete a kickolf circuit at break contacts 146 which is eifective for advancing the main wiper set into engagement with the first terminal set within the selected level in order to start the secondary direction hunting operation. The kick-oli circuit is effective for energizing the winding of hunt assist relay 2-50 from ground through make contacts 124, break contacts 139]] and 146, wiper AW20, the second AWB20 bank contact, conductor XX211, break secondary olfnormal contacts SON117 and overflow contacts OF116, and secondary magnet interrupter contacts S111, the Winding of relay 250, and break release magnet interrupter contacts RL111 to battery. Restoration of relay 140 is further effective for removing dial tone from the calling partys line at break contacts 142 and replaces the dial tone source with ground through break contacts 141.

Relay 250 operates and is effective for energizing magnet S from ground through make contacts 124, break contacts 138, make contacts 251 and 252, and magnet S110 to battery. The main wiper set of the switch thereupon advances within the second level. At the first step of the switch in the secondary direction, the above traced operating circuit for the hunt assist relay 250 is opened at contacts SON117. Thereafter, the energizing circuit for magnet S110 is opened at interrupter contacts S111. If the rst set of contacts within the selected second level is not in use, the sleeve wire bank contact engaged by wiper W213 does not have ground connected to it. Switching relay is thereupon energized and operates from ground through make contacts 124 and SON118, break contacts 145, the winding of relay 130, break contacts OF116 and S111, the winding of relay 250, and break contacts RL111 to battery. The hunt assist relay 250 is so designed that it will not operate in series with the winding of switching relay 130. If the first contact in the selected second level is in use, the Contact engaged by wiper W213 has ground connected to it. This ground connection is extended to the Winding of relay 250, so that the latter will again operate when interrupter contacts S111 reclose. The reenergizing circuit is traced from wiper W213 through break contacts 136, make contacts 122, break contacts OF116 and S111, the winding of hunt assist relay 250 and break contacts R111 to battery. The reoperation of relay 250 again energizes magnet S110 in the above-described manner in order to step the main wiper set one additional step in the secondary direction and therefore into engagement with the next succeeding set of contact wires in the selected level. This interaction between the hunt assist relay and the secondary magnet continues until an idle terminal set, as indicated by the absence of ground on the terminal engaged by wiper W213, is encountered. Thereupon relay 130 operates in the previously described manner.

If all the terminal sets in the selected level are in use, the above described hunting operation continues until the wiper set has been stepped beyond the last terminal set within the selected level and overow contacts OF116 have operated. Operation of break contacts OF116 prevents further stepping in the secondary direction and cates that no idle path is available within the selected level. The calling party may now restore this selector and all preceding equipment including selector S5110 to normal by replacing the receiver or handset on its assetti v'hooksvvitch which 4opens .the-.calling line .loop across conductors T1 and R1.

Restoring the switch to normal Upon the opening of the calling line loop .in the abovedescribed manner, relays 110 and 120 restore to operate release magnet RL110 by connecting ground through break contacts 125 and 139a, make contacts PON119, and the winding of magnet 'RL110 to battery. Energization of magnet RL110 is effective 'for restoring the .switch including the main and auxiliary Wiper sets to normal position, so that the selector is in readiness to receive a succeeding call. Operation of magnet RL110 opens the operating circuit for hunt assist relay 250 at break contacts RL111 and reconnects ground Vto the incoming sleeve conductor through make .contacts RL112 and break contacts 123 in order to prevent the Vreseizure of the `selector prior tothe full restoration of the s'witch to its normal position.

Seizure of an .idle terminal set Assuming that an idle terminal .set and the line connected thereto have been selected, the operation of the 'switching relay 130 in the above-described manner is effective for connecting incoming conductors T1 andRl .through operated `contacts' 132 and 134 Vand wipers W211 and W212 to conductors A1"4 and R4 which are incoming to the `succeeding circuit such as S8220 sho-wn in block diagram form. Operation of relay 130 is also effective for opening the operating circuit for relay 110 at con- ?.tacts 131 and 133. Relay 110 thereupon restores and 1in turn restores relay 12.0 by opening theabove-described `operating circuit at make contacts 112. Operation of .switching relay 13@ also connects the incoming sleeve :conductor through make contacts 137, to the Wiper W213 and the sleeve contact incoming to the succeeding S8220. Apparatus within 88220 is thereafter effective for connecting ground to the sleeve conductor 83 in order to hold relays 130, 88115, and all other preceding equipment after the release of relay 120 has opened the abovedescribed ground connection to the sleeve conductor at make contacts 124.

The operation of switching relay '-130 also .opens ground connected to lamp L110 at contacts 13951. vThereafter lamp L110 remains lighted, but with less brilliance, because ground is now connected to the lamp `through resistor R119 and make contacts 139e. This changing of brilliance from fiull to dim indicates to an .observer that the selector has .been directively pulsed .to an idle succeeding circuit .and serves as an indication 1o show the progress of .a call .through the selector without .the necessity for listening on vconductors T1 and R1.

M zilt-dropback operation.

Within the selector, apparatus is provided for causing the `selector to dropback oneor more times in response to the receipt o particular codes of successive digit impulses transmitted from v.the calling line loop. To this `Aend, various wiring possibilit-ies for the lauxiliary Wire banks AWBZ@ and AWB21 are provided `in addition to -the XX211 conducto-r already described in connection vwith the single digit 'hunting operation. Thus, conductor XX214'is connected to 'the vthird andnfourth terminals of bank AWBZ; conductor XX213 is connected Eto the fifth and sixth terminals; and conductor XX212 is `connected to the seventh lterminal kin bank AWBZU. .Sirnilarly, conductor XX21-0 is connected -to the fourth and sixth terminals within :bank AWBZl. The purposes of these conductors is to control `the apparatus including Acancel A :relay 26@ and cancel fB relay '-270 upon the seflection .of 'the levels. VThe latter relays in turn control .theimeans including release magnet RL110 vfor returning the Wiper sets of the selector .to their inormal positions means :for completing the kick-off circuit in the vmanner to zbe next described. i :Inthe preferred .embodiment of` our invention, provilevel.

sion is made to have the selector drop back in response to the receipt of particular Virst and second digits (different from eachother) transmitted thereto, and to have the selector thereafter select and hunt -Within a level in response tothe receipt of a third digit (of any value). For purposes of demonstration, it is assumed that the rst selected level is the fourth, the second selected level is the fifth, and that the third selected level is any one to which the wipers `have access. We have provided Wire XX214 connected to the fourth terminal in bank AWBZG and XX'ZI'O connected to the fourth terminal in bank AWB21.; similarly, we have provided conductor XX213 connected to the fth terminal of bank AWB201.

.Upon the selection of the fourth level, at the conclusion of a first primary movement of the main Wiper set, wipers AWM and AW21 are advanced to the fourth terminals within banks AWB20 and AWBZ-1, respectively, in the above described manner. At the conclusion of the transmission of the digit to the selector, when delay relay Y140 has vrestored to its normal condition in the previously described manner, relay 270 is operated from ground through conductor XX210, Wiper AW21, break contacts 269c, 148 and 139e, make contacts 113, break contacts 277, and the winding of relay 270 to battery.

4The'operation of relay 270 closes a holding circuit for itself from ground through make contacts 124, break contacts 139i: and 26911, makecontacts 278, and the Winding .of relay 270 to battery. The ope-ration of relay 270 is also efectivefor opening the above-described busy tone connection at break contacts 271 and for substituting a .ground connection for the busy tone connection at make contacts 272. The operation of relay V27d in combination With the presence of yground on conductor XX214 is efective for energizing magnet RLIN in order to cause .the rst dfropback operation of the switch. To this end, upon .the restoration of delay relay 140 toits normal condition at the conclusion of the transmission of the first digit to the selector, the previously mentioned circuit for energizing magnet RL is completed from ground through make contacts 124, break contacts 139b and 146, wiper AW20, conductor XX214, make contacts 276 and 126, break contacts 139a, make contacts` PON119, and the Winding of magnet RL110 to battery. The energization of magnet RL110 is eiective in the previously described manner for dropping the main and auxiliary wiper sets back to their normal positions. Upon the restoration of the selector to its normal position, the previously described operating circuitY for primary delay relay 140` is again completed at break contacts 'PON115 so that the abovedescribed energizing circuit forpprimary magnet P110 is again prepared at make contacts 143. At this point, two-step relay 260 operates through its first step over a circuit and for purposes that are to beexplained 'later in this description. During the presently described operation, the operation of relay 260 is Without effect.

Upon the receipt of the second digit at the selector, the previously described apparatus is again effective to advance the wiper set to the second particular (iifth) The advance of the Wiper set into engagement with the fifth Contact of bank AWBZ() (to which conductor XX213 is connected) is effective in response to the operation of relay 270 for completing a circuit for operating cancel B relay 260. Relay 260 is of the two-step type and isincluded in means for controlling the release magnet RLllil and the kick-o circuit. At this time, relay 260 is operated through its second step over a circuit traced from ground through make contacts 124, break contacts 139b and 146, Wiper AW20, conductor XX213, make contacts 274, the lower Winding of relay 260, and break contacts 265 and RL111 to battery. Relay 260, operated through its second step, opens the operating battery circuit for itself at break contacts 265 and closes a locking circuit for itself which is traced fromy battery through make contacts 264, the lower winding of relay 260, make contacts 267,-break'contacts 139b;'and make -7 contacts 124 to ground. The operation of relay 260 through its second step is further effective for opening the above traced holding circuit for relay 270 at break contacts 266. However, relay 270 continues to be held yin its operated condition owing to the presence of break primary interrupter contacts P111 which are in parallel withthe above mentioned contacts 266. The operation of relay 260 through its second step is further effective for completing a circuit for energizing magnet RL110 from the now-grounded conductor XX213 through make contact 269d, 276 and 126, break contacts 139:1?, make contacts PON119 and magnet RL110 to battery. The energization of magnet RL110 is effective at this time to cause the wiper sets of the switch to restore to their normal positions and to prepare the selector to receive the next transmitted digit.

Upon the restoration of the selector to normal position, primary .delay relay 140 again operates in the above- -described manner to prepare the selector to receive the third digit transmitted over calling line loop. The transmission of the third digit to the selector is effective in the previously described manner to advance the main and auxiliary wiper sets in the primary direction to any one of the levels corresponding to the number of impulses in the third digit impulse train.

Y The third primary movement of the selector following the unlocking operation including the above described first and second dropback operations results in a hunting operation within the level selected by the switch during the third primary movement. In order to make the controlling means including relay 260 effective to complete the kick-off circuit, intermittent operation of the primary interruptor springs including P111 caused by the energization of primary magnet P110 is effective for opening the above-described holding circuit for relay 27 0 at break contacts P111. Relay 270 therefore releases during the transmission of the third and final digit to the selector.

Relay 260 in operated condition is effective in response to the release of relay 270 for energizing the abovedescribed kick-olf circuit including the operating circuit of hunt assist relay 250 as follows: from ground through make contacts 124, break contacts 139b, make contacts 269:1, break contacts 273, 144, SON117, OF116 and S111, the winding of relay 250, and break contacts RL111 to battery. Thereupon the operating circuit for secondary magnet S110 described in connection with single digit operation of the selector is completed, so that the previously described hunting operation is initiated within the third selected level in order to advance the main wiper set Within the latter level until an idle terminal set is engaged or until the switch has advanced to the overflow position.

Single dropback operation In addition to ythe above-described multi-dropback operation, it is desired to have the selector hunt within levels after a primary movement to a different particular level and a subsequent single dropback operation. Accordingly, for purposes of demonstration, we have provided apparatus within the selector which is effective for unlocking the selector with respect to a certain level or levels upon a first primary advance of the sm'tch to a particular `third level different from either of the levels to which the switch is advanced during the multiple dropback operation. Single dropback levels are characterized by the connection of conductors XX210 and XX215 to the `corresponding terminals in wire bank AWB21 and AWB20, respectively. In the drawing, for purposes of demonstration we have shown the XX210 and XX215 conductors connected to the eight auxiliary wire bank terminals.

The single dropback operation is initiated by a primary direction advancement of the selector as described above in connection with single digit operation. At the conclusion of the transmission of the digit to the selector,

when relay 140 releases, relay l270 is operated from `75 grounded conductor 210 over the previously traced circuit. The advance of wiper AW20 to the terminal to which conductor XX215 is connected is effective in respouse to the operation of relay 270 for energizing release magnet RL over thefollowing circuit: from ground through make contacts 124, break contacts 139b and 146, wiper AW20, conductor XX215, break contacts 267, make contacts 276 and 125, break contacts 139er, make contacts PON119, and the winding of magnet RL110 to battery. The energization of magnet RL110 is effective in the previously described manner to restore both the main and auxiliary wiper sets to their normal positions.

The operation of relay 270 is effective in response to the restoration of `the switch to its normal position for operating cancel A relay 260 to its first step or preliminary operated condition over the following circuit: from ground through make contacts 112, break contacts PON115, make contacts 279, break contacts 263, and the upper winding of relay 260 to battery. The upper winding of relay 260 when energized over the above-described circuit is effective for operating preliminary contacts which are characterized in the drawing by a prefix letter X. The other contacts associated with the relay remain upoperated at this time. Thus the operation of relay 260 through its first step is effective immediately for closing a locking circuit for itself from ground through make contacts 124, break contacts 139b, resistor R220, break contacts 269, make contacts 268, the lower winding of relay 260, and break contacts 264 and RL111 -to battery. Resistor R220 limits the current flowing in the holding circuit to the point where rel-ay 260 remains operated in its rst step only.

Thereafter the second digit transmitted to the selector is effective for advancing the switch to the eighth level in `the above-described manner in connection with single digit operation of the switch. The operation of relay 260 through its first step is effective in response to the energization of conductor XX215 (which results from the advance of the wiper AW20 to the eighth level) for completing the kick-olf circuit including the operating winding of hunt ass-ist relay as follows: from ground through make contacts 124, break contacts 139b and 146, wiper AW20, conductor XXZIS, make contacts X266, break contacts SON117, OF116, and S111, the winding of relay 250, and break contacts RL111 to battery, The resulting operation of relay 250 is effective for energizing secondary magnet S110 inthe manner described above in order to Iadvance the main wiper set within the eighth level into engagement with the first contact set. Thereafter relay 250 and magnet S110 operate in the vpreviously described manner yto advance the main wiper set until an idle terminal set is engaged or until ythe wiper set has been `advanced to the overow position.

Summary In the foregoing description, we have shown how the dropback means including the Itwo step cancel A relay 260 is effective in response to ,the advance of the wiper rset to either the fifth or eighth levels for causing a dropback operation of the switch. To this end, we have shown how the advance of the switch to the fifth level is effective for operating cancel A relay 260 through its second step and how the advance of the switch to the eighth level is effective for operating relay 260 -through its Erst step. We have shown how the operation of relay 260 through either its first or second step is effective for energizing the release magnet RL110 in order to cause a dropback operation of the switch. We have shown how relay 260, operated through its first step, is effective in response to a subsequent movement of the switch to the eight level for initiating the secondary direction hunting movement of .the switch and how the relay operated through its second step is effective in response to a subsequent primary movement of the switch to any of the levels of starting the-automatic secondary direction hunting operation any one ofthe levels.

While We have shown and described a specific embodiment of our invention, vother modifications will readily occur to those skilled the art. We do not, therefore, desire our invention lto be limited to the specific arrangement shown and described, and we intend in the appended lclaims to cover all modifications within the spirit and scope Aof our invention.

What is claimed is:

v l. In a dropback selector 'having a vplurality of levels including particular first and second levels, a switch directively operable in a primary direction from a normal position to any one of said levels in a selecting operation, means automatically operable for moving said switch in a secondary direction within the selected one of said levels in order to cause said switch to hunt for an idle line terminated within the selected one of said levels, and means for returning said switch to normal position; the combination comprising: means including a two-stepy relay for causing multi-dropback operation of said selector, said dropback means being controlled by the directive primary movement of said switch to either said first or said second level for selectively operating said relay to its first or second step, respectively, and for thereafter operating said returning means, said relay including means operative upon the first step operation of said relay effective upon the next succeeding primary movement of said switch to said first level for initiating the oper-ation of said automatic secondary direction moving means, said relay including means operative upon the second step operation of said relay effective upon the next succeeding primary movement of said switch to any one of said levels for initiating the operation of said secondary dierction moving means, whereby said selector may be unlocked with respect to said first level only or unlocked with respect to any of said levels.

2. In a dropback selector having a plurality of levels including particular first and second levels, a switch directively operable in a primary direction from a normal position to any one of said levels in a selecting operation, means automatically operable for moving said switch in a secondary direction within the selected one of said levels in order to caluse said switch to hunt -for an idle line terminated within the selected one of said levels, and means for returning said switch to normal position; the combination comprising: means including a two-step relay for causing multi-dropback operation of said selector, said dropback means being operative in response to a first movement of said switch to said first level for operating said relay through its first step and operative in response to an intermediate movement of said switch to said second level for operating said relay through its second step, said relay in said first operated condition being effective in response to a subsequent primary movement of said switch to said first level for initiating the operation of said secondary direction moving means, said relay in said second operated condition being effective in response to -a succeeding primary movement of said switch to any one of said levels for initiating the operation of said secondary direction moving means, whereby said selector is unlocked with respect to said first level upon a first movement of said switch to said first level and is unlocked with respect to any one of said levels upon several consecutive primary movements of said switching including an intermediate movement to said second level.

3. Ina dropback selector including a switch directively operable from a normal position in a primary direction in order to select any one of a plurality of levels where said levels include first, second land third predetermined levels, hunting means for thereafter causing said switch to automatically move in -a secondary direction in order to hunt for an idle line within the selected level, level marking means operated to different positions in accordt Y l0 Y ance with a primarly movement `of said switch, and means Yfor returning said switch to normal; the combination comprising: first relay means for controlling ysaid returning means, said level marking means being effective in response to a primary movement of said switch to said first or said third predetermined levels for operating `said first relay means and for thereupon causing said first relay means to operate said returning means, second relay means operable in a first or a second manner, said second relay means operated in the first manner being eective in response to the operation of said level marking means caused by aprimary advance of said switch to said second level for operating said returning means and thereafter effective in response to a succeeding primary movement of said switch to any one of said levels for operating said hunting means in order to initiate automatic secondary movement of said switch within the subsequently selected level, said first relay means also being operative in response to the operation of said level marking means caused by a first primary movement of said switch to said third predetermined level for operating said returning means, said first relay means in operated condition also being effective in response to the return of said switch to normal for operating said second relay means in the second manner, said second relay means operated in the second manner being effective in response to the operation of said level marking means caused by the primary movement of said switch to said third predetermined level for causing said hunting means to operate in order to intiate the automatic secondary movement of said switch within said third level at the end of two successive movements ofy said switch to s-aid third level.

4. In a dropback selector including a switch, means for directively operating said switch from a normal position in a primary direction in order to select one of a plurality of levels where said levels included first, second, and third predetermined levels, first and second level marking means, each of said level marking means being operative for indicating which of said levels has been selected, means operable to move said switch in a secondary direction, means comprising a hunt assist relay for automatically controlling said secondary movement means in order to cause said switch to hunt for an idle line within the selected one of said levels, a kickoff circuit to be completed at the conclusion of a primary movement of said switch for initially energizing said hunt assist relay, means for returning said switch to normal, and a circuit for energizing said returning means, the combination comprising: means including a first relay for preparing said returning circuit, said first level marking means being operative in response to the advance of said wiper set to said first or said third level for operating said first relay, means for thereafter holding said first relay means in operated condition, said first relay means being operative in response to the operation of said second level marking means caused by the movement of said switch to said first level for completing said returning circuit in order to restore said switch to normal at the conclusion of a first or subsequent primary movement of said switch to said first or said third level, means including a second relay having a normal and preliminary and fully operated conditions for controlling said kickofr` circuit, said first relay being operative in response to the return of said switch to normal for operating said second relay to said preliminary operated condition and operative in response to the operation of said second level marking means caused by the movement of said switch to said second level for operating said second relay to said fully operated condition, said second level marking means being effective in response to the operation of said first relay and to the full operation of said second relay for completing said returning circuit in order to return said switch to normal after a second primary movement to said second level, said primary moving means being effective in response to the operation of said second relay tot 1-1` its fully operated condition for opening said rst relay holding circuit inorder to release said rst relay during a third primary movement of said switch which follows first and second primary movements to said rst and said second levels, respectively, said second relay in preliminary operated condition being eiective -in response to the operation of said second level marking means caused by an advance of said switch to said third level for completing said kickoff circuit over a rst route, said second relay in fully operated condition being eective in response to the release of said rst relay for completing said kickoff circuit over a second route whereby said switch may be advanced Within said third level with two consecutive movements to said third level and may be advanced within any one of said levels following rst and second primary movements to said first and said second level, respectively, followed by a thirdadvance to any 'one of said levels.

Carson et al. July 4, 1950 Pharis A Ian. 14, 1958 

